Measurement of microbial biomass or other soil analytes is difficult because of the large amount of particulate matter that is irrelevant to the measurement of these analytes and because the color of an extract precludes assaying for analytes by methods such as spectrophotometery, turbidity, nephalometry and visual comparison. One of the most difficult parameters to measure is Microbial Biomass which is an excellent indicator of soil and compost quality and is a predictor of soil fertility. Soil microbes recycle the organic matter in soil and convert it into forms that can be utilized by plants. Bacteria represent the majority of the microbial life in soil and serve as the bottom rung of the microbial soil food chain which consists of bacteria, fungi, protozoa, algae and nematodes. Abundant microbial life indicates that the nutrient levels of soil are sufficient and balanced and that there is an absence of significant levels of deleterious or poisonous substances such as heavy metals or high concentrations of salts.
Studies have revealed that the ratios and diversity of the various microorganisms present in soil varies with different soil types and is a predictor of soil fecundity. However, tests and test standardization to establish the microbial content of soils have not been extensively developed (Compost Quality in America, Woods End Research Laboratory, Inc., Report (2000)).
Currently, several laboratories provide commercial in-house services to estimate the numbers of various different types of microbes in soil. These estimates are based upon laboratory tests that are costly, labor intensive and results are not available for 7-21 days. Because only about 10% of soil microbes can be cultured and then only with great difficulty and time, analyses must be performed by direct counting using a microscope and a diluted sample on a slide. The slide can be difficult to read because soil particles predominate, and expertise is required to distinguish between bacteria, fungi and protozoa, rendering these tests prohibitively expensive for use as routine quality control. In addition, soil samples must be transported to the laboratory for analysis and it can take days or weeks for the results to be reported. These methods are not practical for estimation of the microbial content of composts and compost extracts, which must be used within one or two days of formulation. Further, the results are not consistant from lab to lab, due to the subjective nature of visual counts.
Bacteria are typically the most abundant and diverse microbial component of soil. A Standard laboratory technique for quantitation of bacteria is based upon spectrophotometric measurement of turbidity within a solution. However, this method is problematic for measurement of the bacterial content of soil samples because the particles and pigments in soil also contribute to turbidity, reflectance and/or transmittance measurements. In addition, many microbes in soil are firmly attached to the soil particles and do not readily go into solution. Further, it is not practical to apply these methods to a field test to assess microbial biomass in soil because of the need for a turbidometer or spectrophotometer which would require calibration, precluding rapid and efficient use in the field. Accurate estimates of microbial numbers are required on-site and within a few minutes of sampling to determine whether a new treatment increased microbial growth or how much to dilute a compost extract.
Therefore it is an object of the invention to provide methods and reagents for measuring the microbial content of soil that are convenient for use in the field setting.
It is a further object of the invention to provide time effective and cost effective methods for providing an estimate of microbial numbers within a soil sample.